In the area of vaccinology, antigens are introduced into a host in a manner so as to stimulate an immune response to the antigen and therefore to the potential pathogen. The induction of an immune response depends on many factors among which are believed to be the chemical composition, characteristics and configuration of the antigen, the health and immune competence of the host, and the manner of delivery and administration of the antigen.
An immune response has many facets, some of which are exhibited by the cells of the immune system, (e.g., Dendritic cells, B-lymphocytes, T-lymphocytes, macrophages, and plasma cells). Cells of the immune system participate in the immune response through interaction with antigens or other cells of the immune system, the release of cytokines and reactivity to those cytokines. Adaptive (acquired) immune response is conveniently (but arbitrarily) divided into two main categories—humoral and cell-mediated. The humoral component of the immune response includes production of antibodies specific for the antigen. The cell-mediated component includes the generation of delayed-type hypersensitivity and cytotoxic effector T-cells specific to the antigen.
Adjuvants are substances used to potentiate an immune response when used in conjunction with the antigen. The use of an adjuvant in a vaccination protocol may, for example, elicit an immune response that is faster or greater than would be elicited with antigen alone. In addition, adjuvants may be used to direct the immune response to specific immunological pathways and to serve as a delivery vehicle for the antigen.
Liposomes and liposomal formulations are examples of adjuvants. Typically liposomes can be loaded with the antigen(s) and/or other immunomodulatory compounds, or the liposomes themselves may serve as standalone adjuvants. The antigens and/or other immunostimulatory compounds may be encapsulated in the interior of the liposome, and/or they can be attached to the liposome or incorporated into the lipid bilayer.
The factors influencing the suitability of a given liposome as a delivery vehicle in a given system presentation remain unclear. Thus there is still a need for delivery vehicles, which provide an improved efficacy. Such an improved delivery is particular for the administration of molecules which stimulate and/or elicit an immune response, for example, antigens and immunomodulators.